The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, CVVT systems are used in vehicles with the purposes of reducing exhaust gas, improving fuel efficiency, and enhancing output. Research on intermediate phase CVVT systems has recently been conducted with the goal of overcoming limits related to the responsiveness of a conventional CVVT system and a restrictive operation section. In the case of intermediate phase CVVT systems, the position of a cam is controlled at an intermediate position rather than a most advanced (intake) position or a most retarded (exhaust) position. Therefore, responsiveness is comparatively high, and the range within which the cam is available can be increased. Thereby, fuel efficiency can be improved, and the amount of exhaust gas can be reduced.
Meanwhile, in an intermediate phase CVVT system, while the RPM of an engine is reduced, a lock pin installed adjacent to a rotor is locked to a lock-pin hole disposed at a medial position between the advanced chamber and the retarded chamber, thus being ready for subsequent ignition of the engine. Here, automatically locking the lock pin to the lock-pin hole while the RPM of the engine is reduced refers to a ‘self-lock’ state.
Self-locking functions to enable the CVVT to be mechanically returned to an accurate position without separate control so that reliable operation of the engine can be ensured in a non-operation area of the CVVT system, that is, when the vehicle is in an idle or ignition state.
However, we have discovered that if the valve timing remains at the most retarded position rather than returning to an intermediate phase, a surge tank is increased in pressure to the level of atmospheric pressure, rather than creating a vacuum when the vehicle is in an idle state. Therefore, a problem of deterioration of braking performance using the vacuum in the surge tank is caused.
Furthermore, we have discovered that if the valve timing remains at the most advanced position rather than returning to the intermediate phase, valve timing overlap between an intake valve and an exhaust valve is excessively frequently caused. Thus, the reliability of the operation of the engine is reduced. In addition, a problem of vibration of the engine is exacerbated. In some cases, a problem of engine stalling may be caused.
In other words, in the intermediate phase CVVT system, we have discovered that when the self-lock function of the lock pin is automatically conducted, as under normal conditions, and the rotor and the lock pin are thus in the most advanced or retarded position, a problem of engine stalling or a problem of malfunction of the brakes because of a lack of negative pressure is caused.
Furthermore, we have discovered that if a difference in oil pressure between the advanced chamber and the retarded chamber is caused when the locked state of the lock pin is released, side force is applied to the lock pin, thus causing a problem of the lock pin being undesirably removed from the locking hole. Further, once fatigue accumulates on the lock pin, a problem of damage to the lock pin may be caused.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the foregoing is already known to those skilled in the art.